The phrase “mobile telecommunications system” generally refers to any telecommunication system which enables a wireless communication connection between a mobile station (MS) and the fixed parts of the system when the user of the mobile station is moving within the service area of the system. A typical mobile communication system is a Public Land Mobile Network (PLMN). The majority of mobile telecommunication systems in use to date belong to second generation systems such as the well-known Global System for Mobile Telecommunications (GSM) system commonly used in Europe and elsewhere, including the United States. The present invention applies particularly to general packet radio service (GPRS) which forms part of the architecture of Universal Mobile Telecommunications System (UMTS), a third generation system which merges mobile telephony with data communications, especially those for use with the global communications network commonly called the Internet. Data communications can also include multi-media services associated with the Internet. Such services, including Internet real-time services, have gained popularity over the last several years. Internet protocol (IP) telephony and different streaming applications such as audio streaming and video streaming are already quite common on the Internet. In addition, the demand for wireless access to these real-time services is expected to grow at an exponential rate over the near term. Packet switched wireless networks such as GPRS are designed to provide data services such as Internet services, in a cost effective manner. In GPRS, the channels are not dedicated to one user on a continuous basis but are shared between multiple users. This procedure facilitates efficient data multiplexing. However, GPRS was not originally designed for transferring delay sensitive real-time data, such as IP telephony sessions. In general, it was not specifically designed for applications that transfer data that have relatively short inactive periods (no data to be transmitted) between active data transfer periods. For this reason, GPRS currently contains various technical solutions that only partially meet the requirements with regard to real-time traffic. As defined herein, the phrase “specific traffic class” corresponds to data transfer for which the network resources are not to be released during possible inactive periods between active periods. An example of such is a conversational voice connection or an interactive connection e.g. telnet. It is very beneficial in UMTS, but it can also be used in interactive data transfer applications, e.g. telnet.
In order to better understand the problems of prior art solutions as well as the idea of the present invention, the structure of a third generation digital cellular radio system is first described and GPRS is then described in more detail.
FIG. 1a shows a version of a future cellular radio system which is not entirely new with respect to the known GSM system, but which nevertheless includes known elements and new elements. The terminals are connected to the radio access network (RAN) which includes the base stations and the base station controllers. The core network of a cellular radio system comprises mobile services switching centers (MSCs), other network elements (in GSM, e.g. SGSN and GGSN, that is, Serving GPRS Support Node and Gateway GPRS Support Node) and related transmission systems. According to GSM+ specifications developed from GSM, the core network can also provide new services.
A new technology, Enhanced Data Rates for GSM Evolution (EDGE) will increase the network capacity and data access rates of both circuit switching and packet switching so as to meet expected demands of wireless multimedia applications and more market deployment. The transmission speed of circuit switching is increasing with the introduction of High Speed Circuit Switched Data (HSCSD) while packet data rates are being provided by General Packet Radio Services (GPRS). EDGE, a new radio interface technology with enhanced modulation, increases the HSCSD and GPRS data rates by up to three fold. EDGE modulation increases the data throughput provided by the packet switched service even over 400 kbit/s per carrier. Similarly, the data rates of circuit switched data can be increased, or existing data rates can be achieved using fewer timeslots, saving capacity. Accordingly, these higher speed data services are referred to as EGPRS (Enhanced GPRS) and ECSD (Enhanced Circuit Switched Data).
This combination of EGPRS and HSCSD in a network is known as GERAN, GSM EDGE Radio Access Network. FIG. 1c illustrates GERAN, including the EGPRS and ECSD branches of the network. Officially GERAN is a term used to describe a GSM and EDGE based 200 kHz radio access network. The GERAN is based on GSM/EDGE release 99 and covers all new features for GSM Release 2000 and subsequent releases, with full backward compatibility to previous releases.
In GERAN, packet voice service using e.g. AMR (Adaptive Multirate Codec) may be implemented. Such services represent a type of real-time application that typically has periods of silence (no speech). Procedures for handling such applications are required.
FIG. 1b shows an architecture of a general packet radio service (GPRS). As explained, earlier GPRS is a new service that is currently based on the GSM system but the general principles discussed herein can be applied to GRAN (General Radio Access Network). GPRS is one of the objects of the standardization work of the GSM phase 2+ and UMTS at the ETSI (European Telecommunications Standard Institute) and 3GPP. The GPRS operational environment comprises one or more subnetwork service areas, which are interconnected by a GPRS backbone network. A subnetwork comprises a number of packet data service nodes (SN), which in this application will be referred to as serving GPRS support nodes (SGSN) 153, each of which is connected to the mobile telecommunications system (typically to a base station through an interworking unit) in such a way that it can provide a packet service for mobile data terminals 151 via several base stations 152, i.e. cells. The intermediate mobile communication network provides packet-switched data transmission between a support node and mobile data terminals 151. Different subnetworks are in turn connected to an external data network, e.g. to a Public Data Network (PDN) 155, via GPRS gateway support nodes GGSN 154. The GPRS service allows the provision of packet data transmission between mobile data terminals and external data networks when the appropriate parts of a mobile telecommunications system function as an access network.
In order to access the GPRS services, a mobile station first makes its presence known to the network by performing a GPRS attachment. This operation establishes a logical link between the mobile station and the SGSN, and makes the mobile station available for SMS (Short Message Services) 158, 159, over GPRS, paging via SGSN, and notification of incoming GPRS data. More particularly, when the mobile station attaches to the GPRS network, i.e. in a GPRS attachment procedure, the SGSN creates a mobility management context (MM context). Also, the authentication of the user is carried out by the SGSN in the GPRS attachment procedure. In order to send and receive GPRS data, the MS activates the packet data address that it desires to use by requesting a PDP activation procedure (Packet Data Protocol). This operation makes the mobile station known in the corresponding GGSN, and interworking with external data networks can commence. More particularly, a PDP context is created in the mobile station and the GGSN and the SGSN. The packet data protocol context defines different data transmission parameters, such as the PDP type (e.g. X.25 or IP), the PDP address (e.g. X.121 address), the Quality of Service (QoS) and the NSAPI (Network Service Access Point Identifier). The MS activates the PDP context with a specific message, Activate PDP Context Request, in which it gives information on the TLLI, the PDP type, the PDP address, the required QoS and the NSAPI, and optionally the access point name (APN).
FIG. 1b also shows the following GSM functional blocks; Mobile Switching Center (MSC)/Visitor Location Register (VLR) 160, Home Location Register (HLR) 157 and Equipment Identity Register (EIR) 161. The GPRS system is usually also connected to other Public Land Mobile Networks (PLMN) 156.
Functions applying digital data transmission protocols are usually described as a stack according to the OSI (Open Systems Interface) model, where the tasks of the various layers of the stack, as well as data transmission between the layers, are exactly defined. In the GSM system phase 2+, which is observed herein as an example of a digital wireless data transmission system, there are five operational layers defined.
The mobile station MS must include a higher-level control protocol 212 and a protocol 213 for serving higher-level applications, of which the former communicates with the RRC layer 206 in order to realize control functions connected to data transmission connections, and the latter communicates directly with the LLC layer 204 in order to transmit such data that directly serves the user (for instance digitally encoded speech). In a mobile station of the GSM system, the blocks 212 and 213 are included in the above-mentioned MM layer.
In GPRS, a Temporary Block Flow (TBF) is created for transferring data packets on a packet data channel. The TBF is a physical connection used by the two Radio Resource (RR) peer entities to support the unidirectional transfer of Logical Link Control (LLC) Packet Data Units (PDU) on packet data physical channels. The TBF is normally always released when there is no data to be transmitted. Such a release creates a problem in voice services and other real-time services such as streaming audio or video when silent periods can occur from time to time. It is also a problem in general where the application has relatively short inactive periods between active transmission periods. Such applications can include telnet and web browsing. During these silent or “passive” periods no data is transferred and the TBF is thus normally released. The TBF setup procedure is likely to be too long in order to be set up quickly enough when the active period resumes, which results in undesirable voice quality.
An example of the resource allocation in the GPRS of the current GSM Phase 2+ specification is next described in more detail.
In the GSM Phase 2+ the uplink resource allocation is currently specified as follows: The Mobile Station (MS) requests uplink radio resources by sending a PACKET CHANNEL REQUEST message to the network. Various access type values are specified for the request message. For data transfer ‘one phase access’, ‘two phase access’ and ‘short access’ type values are defined. Using ‘short access’ type value, the MS may request the radio resources to transfer only a few RLC data blocks, and therefore it is not applicable for transferring continuous data flows.
When a network receives a PACKET CHANNEL REQUEST message indicating one phase access, it may allocate radio resources on one or several Packet Data Channels (PDCH). The allocation is based on information included in the request message. The following table shows an example for an 11 bit message content of a PACKET CHANNEL REQUEST message:
bitsPacket Channel1110987654321Access0mmmmmpprrrOne Phase AccessRequest<MultislotClass: bit(5)><Priority: bit (3)><RandomBits: bit(3)>100nnnpprrrShort AccessRequest<NoOfBlocks: bit(3)><Priority: bit (2)><RandomBits: bit(3)>110000pprrrTwo Phase AccessRequest<Priority: bit(2)><RandomBits: bit(3)>110001rrrrrPage Response<RandomBits: bit(5)>110010rrrrrCell Update<RandomBits: bit(5)>110011rrrrrMobility Manage-ment Procedure<RandomBits: bit(6)>110100rrrrrSingle Block With-out TBF Establish-ment<RandomBits: bit(5)>All othersReserved
An 11 bit PACKET CHANNEL REQUEST message indicating one phase access has a field of 5 bits describing the multislot class of the mobile station, a field of two bits indicating requested priority and a field of three bits describing random reference (random mobile station identification information).
The following table shows an example for an 8 bit message content of a PACKET CHANNEL REQUEST message:
bits87654321Packet Channel Access1mmmmmrrOne phase Access Request<MultislotClass: bit (5)><RandomBits: bit (2)>00nnnrrrShort Access Request<NoOfBlocks: bit (3)><Randombits: bit (3)>01000rrrTwo Phase Access Request<RandomBits: bit (3)>01001rrrPage Response<RandomBits: bit (3)>01010rrrCell Update<RandomBits: bit (3)>01011rrrMobility Management Procedure<RandomBits: bit (3)>01100rrrSingle Block Without TBFEstablishment<RandomBits: bit (3)>All othersReserved
An 8 bit Packet Channel Request message indicating one phase access has a field of 5 bits describing the multislot class of the mobile station and a field of two bits describing random reference. The information about the allocated radio resources is sent to the Mobile Station with a PACKET UPLINK ASSIGNMENT message.
When a network receives a PACKET CHANNEL REQUEST message indicating two phase access, it may allocate limited radio resource on one packet data channel. The allocated radio resources are transmitted to the mobile station with a PACKET UPLINK ASSIGNMENT message. After this allocation the mobile station transmits a PACKET RESOURCE REQUEST message to the network by using the allocated radio resource. The message defines more accurately the required radio resources, e.g. requested bandwidth and priority, and the radio capability of the mobile station. Based on the information received in the PACKET RESOURCE REQUEST message, the network may assign one or several packet data channels to the TBF and informs the assigned radio resources to the mobile station with a PACKET UPLINK ASSIGNMENT message.
In such a configuration, the request of resources is made using the GPRS control channel as an example. There are also other ways of requesting resources in case the cell does not include a GPRS control channel (even if it supports GPRS). In this case the resource request can be made using a GSM control channel.
In the prior art the uplink radio resource allocation could cause the following problems:
If the priority field included in the PACKET CHANNEL REQUEST and the PACKET RESOURCE REQUEST messages does not define the characteristics of the data to be transmitted (e.g. delay sensitive real-time traffic), the network might not be able to provide the needed radio resources for the MS. Thus, e.g. transferring speech using the GPRS might not reach a sufficient quality.
The default RLC mode is an acknowledged mode in one phase access. Since real-time traffic would be transferred using unacknowledged RLC mode, two phase access should be used. Using two phase access, additional radio resource request information may be given to the network. However, two phase access causes additional delay to the channel assignment procedure, because the mobile station has to send two request messages to the network instead of one. In spite of the additional radio resource request information it is not guaranteed that the network is able to provide the needed radio resources for the mobile station transferring delay sensitive real-time traffic.
When allocating radio resources for uplink transfer, downlink radio resources cannot be allocated simultaneously, because the downlink Temporary Block Flow (TBF) cannot be created without downlink packets. Thus it is possible, when the mobile station is to receive a downlink packet, the network is unable to assign radio resources for the transfer of the packet.
Downlink radio resource allocation is currently specified as follows: When the network receives data for a mobile station which has no assigned radio resources and whose cell location is known, the network assigns radio resources on one or several packet data channels by transmitting a PACKET DOWNLINK ASSIGNMENT message to the mobile station. When the mobile station receives the assignment message, it starts listening to the allocated packet data channels for Radio Link Control (RLC) data blocks.
In downlink radio resource allocation, the following problems may arise:
If information attached to data (coming from the SGSN) does not define the characteristics of the data to be transmitted (e.g. delay sensitive real-time traffic), the network may not be able to provide the needed downlink radio resources for the MS.
Also if there is a need to transfer e.g. delay sensitive real-time traffic in both directions, downlink and uplink, the mobile station may request uplink radio resources only when the network assigns sending permission to the mobile station. This may cause a delay of a variable amount of time, such as several seconds.
When allocating radio resources for downlink transfer, uplink radio resources cannot be allocated simultaneously because the uplink Temporary Block Flow cannot be created without uplink packets. Thus it is possible, that the mobile station may request uplink radio resources but the network is unable to assign the requested radio resources.
Uplink radio resource deallocation is currently specified as follows: Every uplink RLC data block includes a countdown value (CV) field. It is specified in reference [1] (see Table 1) that the CV shall be 15 when the mobile station has more than BS_CV_MAX (broadcast parameter) RLC data blocks left to be transmitted to the network. Otherwise the mobile station indicates to the network the number of remaining RLC data blocks with the CV field. The last RLC data block is sent to the network with the CV value set to ‘0’. Reference [1] also defines that once the mobile station has sent a CV value other than ‘15’, it shall not enqueue any new RLC data blocks; meaning that the new RLC data blocks shall not be sent during the ongoing TBF. Once the network receives RLC data block with the CV field set to ‘0’, the TBF release procedures are initiated.
In uplink radio resource deallocation, the following problems may arise:
If e.g. delay sensitive real-time data is transferred over radio interface according to current GPRS rules, the mobile station has to establish several TBFs per session, because during the passive periods the mobile station has no RLC data blocks to send to the network and thus the CV value ‘0’ terminates the uplink TBF. Because the TBF setup procedures takes time, delay sensitive traffic cannot be transmitted with good quality. Also, there are no guarantees that free radio resources are always available when the mobile station requests uplink radio resources.
Downlink radio resource deallocation is currently specified as follows: Every downlink RLC data block includes a Final Block Indicator (FBI) field in the RLC header. Reference [1] defines that the network indicates to the mobile station the release of the downlink TBF by setting the FBI field to ‘1’. The network sets the FBI field to ‘1’ when it has no more RLC data blocks to send to the mobile station. After receiving RLC data block with FBI field set to ‘1’ the mobile station shall acknowledge to the network that it has received the FBI information. When the network receives the acknowledgement message, the TBF is released.
In downlink radio resource deallocation, the following problems may arise:
If e.g. delay sensitive real-time traffic is transferred over radio interface according to current GPRS rules, the network has to establish several TBFs per session, because during the passive periods the network has no RLC data blocks to send to the mobile station and thus the FBI value ‘1’ terminates the downlink TBF. Also, there are no guarantees that free radio resources are always available when the network tries to allocate downlink radio resources.
Problems also occur in assigning uplink and downlink sending permissions: If e.g. delay sensitive real-time data traffic is transferred on packet data channel/channels (PDCH), it is not guaranteed that adequate sending permissions are given in order to transfer the data, because the current network may not have knowledge about the characteristics of the transferred data (e.g. delay sensitive data).
A further problem with the prior art specification is related to the feature that the network assigns transmission permissions for uplink and downlink directions independently, i.e. controls which mobile station receives data next and which mobile station may send data next. However, some types of application generated data, e.g. delay sensitive data associated with speech, have strict delay requirements. Consequently, whenever such a delay sensitive data user has something to transmit, it must be able to do so in order to maintain an acceptable service level. If more than one user is allocated to the same packet data channel it is probable that at some point two or more users will need to transmit simultaneously, and just one can be served on the channel. In speech conversations a large proportion of the connection time is silence. Thus it would be possible to statistically multiplex more than one speech user for one packet data channel. The GPRS channel reservation system, however, is not elaborate enough to support this need. Therefore only one user of delay sensitive data transfer can be allocated for one packet channel, which means that the usage of the channel capacity is not optimized.
When the network notices that a mobile station wants to send e,g, delay sensitive data in the uplink direction the network reserves as much uplink resources to the mobile station as is requested. This naturally requires that the network has the required resources available. Such allocation may mean that the packet data channel is dedicated temporarily to a single mobile station in the uplink direction. During passive periods in such uplink delay sensitive data transfer, the network may assign uplink sending permissions of the allocated channels to other mobile stations. Since the mobile station transferring e.g. delay sensitive data reserves the uplink capacity of the packet data channel, other mobile stations that are allocated to the same packet data channel cannot be assigned a sending permission to determine whether they have data to send in the uplink direction. Also, if more than one mobile station allocated to the same packet data channel needs to send e.g. delay sensitive data at the same time, only one can be served. Therefore the network is forced to restrict the number of mobile stations transferring e.g. delay sensitive data according to the number of packet data channels in order to provide acceptable service quality.